The main problem with this is that this means that when a test enables a language or module through the UI and locale.module is enabled, it tries to download translations. I think that might be slowing down a few tests right now (assumption, have not checked if that is actually true).
Fixing it is easy.
- Verify that this is actually the case (Run a test that tests the language UI locally, look at the debug output check if there is a translations downloaded message)
- Define a setting (config(), not variable_get()), default it to TRUE. No UI necessary at this point (can be discussed separately)
- Adjust testing profile .install to set it to FALSE.
- Verify that the translations are still downloaded by efault for you (a re-install might be necessary to update the config defaults)
- Re-run test and verify that there is no such message anymore. Write a simple test for this (add an assertNoText or similar)